mavsdk_tests: refactor/cleanup
mavsdk_tests: refactor/cleanup

This splits the main function which has become way too long.

krbeverx/Firmware,acfloria/Firmware,krbeverx/Firmware,krbeverx/Firmware,PX4/Firmware,PX4/Firmware,acfloria/Firmware,acfloria/Firmware,acfloria/Firmware,PX4/Firmware,krbeverx/Firmware,acfloria/Firmware,PX4/Firmware,PX4/Firmware,krbeverx/Firmware,PX4/Firmware,acfloria/Firmware,PX4/Firmware,krbeverx/Firmware,krbeverx/Firmware,acfloria/Firmware